This shows a longitudinal traveling wave, such as a sound wave in air. The spots are representative regions of air (not really molecules, whose high-speed random motion is not shown). Note that each region simply oscillates back and forth about a central location. All regions are doing exactly the same thing, yet there is an obvious flow of something from left to right. This flow doesn't carry the medium with it, but it does carry energy. It also carries information, such as amplitude and frequency. Were it modulated in some clever way, it might carry more information, like your voice.